The invention relates to an optical multiplexer for transmitting light supplied by a plurality of input optical fibers to a single output optical fiber. The multiplexer comprises an input lens system and an output lens system for imaging end faces of the input fibers onto the end face of the output fiber. The end faces of the input fibers are situated in the focal plane of the input lens system.
An optical multiplexer of this kind is known from an article by T. Miki et al entitled "Viabilities of the Wavelength-Division-Multiplexing Transmission System Over an Optical Fiber Cable" IEEE Transactions on Communications, Volume COM-26, No. 7, July 1978, pages 1082-1087. For each input fiber the multiplexer described in the article comprises an input lens whose optical axis must be aligned with respect to the optical axis of the optical fiber, and an output lens which is arranged between the input lenses and the output fiber. The optical axis of the output lens and the optical axis of the output fiber should coincide. It will be evident, even though the mechanical construction of the published multiplexer is not described, that a comparatively large number of accurate positioning operations will be necessary in this multiplexer (for example, each fiber must be positioned with respect to the associated input lens). Furthermore, the multiplexer introduces a comparatively high attenuation (12 dB) in the path of the optical signals to be transmitted.